Tissue adhesion which is a physiological action as generated after a surgical operation is defined as abnormal binding between a surrounding tissue and an organ or the like, which is caused from the production of a collagen fiber by a fibroblast as generated following a tissue damage. It is considered that such adhesion occurs at a probability of 90% after the operation, and in the case where a pain, a biofunctional disorder, or the like is caused, a patient is accompanied by mental or physical pain, resulting in a problem.
In order to solve this problem, there have hitherto been made a number of studies. For example, in order to minimize the adhesion formation, water-soluble anti-adhesion membrane such as a sodium alginate aqueous solution and a sodium hyaluronate aqueous solution were used. However, while these materials have some anti adhesive effect, because of their water solubility, they also flow out of the site where prevention of adhesion is required, they do not retain in a necessary place, and they have a possibility to cause undesired adhesion in a normal area.
For that reason, in order to separate a damaged tissue from other tissues, anti-adhesion membrane made of, as a physical barrier, a material such as silicone, vaseline, and polytetrafluoroethylene are studied. Since such a material is a non-bioabsorbable material, while it is provided with a sufficient action as a barrier, there were involved problems such as a risk of an immune response due to long-term retention in the body and a necessity of a second operation for taking out it after cure.
In order to solve these problems, anti-adhesion membrane using a natural polymer which is a bioabsorbable material were developed.
Specifically, an anti-adhesion membrane using oxidized cellulose is known. In the case of applying a sponge or knit made of oxidized cellulose, since fibrious cells are liable to pass through voids and migrate, there was involved a problem of causing adhesion. In order to prevent this, anti-adhesion membrane made of sodium hyaluronate and carboxymethyl cellulose are developed and used. However, since these materials have high water absorption, there is involved a problem such that they are swelled by liquid of surgical instruments or organs other than a wound area so that handling properties are poor.
An anti-adhesion membrane is desired to have a shape in which circulation of fibrious cells from one tissue to other tissue does not occur and is also desired to have biodegradability and high operability.
JP-A-2000-197693 discloses a porous anti-adhesion membrane made of a copolymer of lactic acid and caprolactone.
JP-A-2001-157574 describes a film having a honeycomb structure as prepared from a polymer containing a biodegradable polymer having added thereto 1 to 50% of an amphiphilic polymer having a hydrophilic acrylamide polymer as a principal chain skeleton and having both a dodecyl group as a hydrophobic side chain and a lactose group or a carboxyl group as a hydrophilic side chain and a production process thereof.
However, though the base material polymer as used herein is a polymer having high biocompatibility, there is concern that the amphiphilic polymer might be decomposed into acrylamide derivatives, and it is hard to say that the derivatives are always safety against a living body. If possible, it is desired that the amount of use of such an amphiphilic polymer is controlled at a low level as far as possible.
In this way, for the purpose of applying to a biotissue, in the case of using a film having a fine structure, biocompatibility becomes a big problem. For that reason, not only a polymer to be used but also a reagent for forming a fine structure, namely a surfactant such as amphiphilic polymers, is desired to have biocompatibility and safety against a living body. For the purpose of achieving this, it is also desired from the viewpoint of securing safety to increase the content of the polymer and to control the amount of use of the surfactant.
In the existing circumstances, any anti-adhesion membrane which has adequate biodegradability and biocompatibility, is excellent in handling properties and exhibits a satisfactory adhesion preventive effect stably over a desired period of time does not exist, and its appearance is being demanded.